Nhxno



:temperatures (up to 2,000' F.).

James G. MacArthur, Baxter Springs, Kans., assignor to Spencer Chemical Company, a corporation of MISSOUI'I No Drawing. Application April 19, 1957 Serial No. 653,763

20 Claims. Cl. 106-72) This invention is related to the manufacture of kilnfired ceramic products, such as brick and Me. More 2,899,324 Patented Aug. 11, 195i) a 2'1 v proach has been more finely to divide the clay so. that more surface is exposed to oxidation, but this has not proven too successful. ;T.

- Agrecentlyproposed method of;controlling coring, in volves the addition of ammonium chloride to the clay mix prior to firing. It is stated that the ammonium chloat ride lowers-the'temperature of dissociation of the sulfide compoundsthought to be responsible in main for; coring, thus allowing them to be oxidized in a shorter period of ,time, However, ammonium chloridefused separately does not give good control in, many clays and. in fact has adverse effects when; used with some specifically, this invention is related to the manufacture P1 of improved ceramic products through the use of hexamethylenetetramine or hexamethylenetetramine in combination with inorganic ammonium salts effectively to control coring, and thereby give a product possessing improved strength and dimensional properties. I

In the manufacture of brick and tile products, the finely divided clay or shale is mixed with varying amounts of water to provide the proper plasticity,formed into the desired shape, dried and fired in either periodic (batch) or tunnel (continuous) kilns to form the finished clay products. The word clay as used herein is intended to embrace both shale and clays, such assurfac'e clays and fire clays. t E "During the firing process, various clay components arebelieved to be oxidized by the kiln gases and the clay then indurated (or hardened) by long exposureto higher Improper firing, particularly with clays high in sulfur and/or carbon content, often results in an undesirable phenomenon, termed I coring, which seriously affects strength and dimension- 1 al properties in the final product. Coring, as the name implies, is characterized by a black, blue, grey,

brown or red core in the finished clay product which may extend completely to the surface. Black'coring is generally the most severe. 'Uponoxidation, which occurs during the firinggthe black compounds change from the characteristic black or dark color 'to redor buff color. Under certain conditions, the complete oxidation of the dark colored -compounds appears to be relatively easy to accomplish. Under'other conditions the black color appears fixed and extremely diffcultif not impossible to oxidize. The exact conditions under which the black core becomes fixed are unknown, but'the phenomenon appears to be associated with the-deformation or and tile industry, is a discoloration which results-from a bleeding through of the core. "Sucha discoloration plastic point of the clay or shale, wherein the material 1, fb'eco'mes'glass-like befo're'oxidation is complete. A seconda'ry disadvantage of coring, particularly in the brick is very unsightly, for instance, on the brick and mortar joints of a brick wall.

" Coring can be successfully controlled in certainclays by lengthening the firing cycle so that oxidation is complete. In other clays, coring cannot be economically controlled by lengthening the firing cycle. The control" I of coring by chemical additives is highly desirable in either case so that the firingcyc'le canbejshor'tened and kiln production substantially increased.

Many attempts have been made in he past to control coring,.such .as by addingpre-roasted clay to the clay so that part 'of the oxidia'tion is already accomj 'plished. 'Although the final .fi'ringcycle islreducedsornewhat, the total energy requirements for firing ,are the same, hence 'noadvant a'ges aregained. ape

ride alone. v V I l [I-Iexamethylenetetramine, usually'known as hexamine,

clays, particularly ,with respect to the structural proper: ties and the water absorption properties of the resulting products. Also, because of its inherent acidity amv monium chloride causes serious corrosion problems in the'metal' clay products manufacturing equipment and produces a prominent discoloration throughout light-col ored clay products. Because of these critical shortcom ings, ammonium chloride has had very limited application intheindustry.. I t e I 5 In attacking; the above-described problems of the bri ck,tile and relatedindustries, I have discovered that hexamethylenetetramine, separately and in various com; binations'with inorganic ammonium salts, will effectively controlcoring in kiln-firedfclay and shale products. The inorganic ammonium salts that may best be used iricl'nde, the common inorganic ammonium salts such amm nium nitrate, ammonium sulfate and ammonium phosphate. Ammoniu mf.chloride' may also be usedin combin tion with hexamethylenetetramine elfectively, to control coring. Although thi's additivecombination retains the corrosive characteristics of the ammonium chloride, it is 'lesscorrosive than ammonium chloride alone. i

Surprisingly, the combination of ammonium chloride 'withjhexamethylenetetramine is much more eflectivein the control of coring than ammoniumchldmay be produced by the reaction of an aqueous solution of formaldehyde with ammonia The reaction maybe represented as follows:

I '6cH,0{4 H,- cH, ai -611,0' Hexamine is a crystalline solid which is readily soluble in water sublimeswith'slightdecomposition upon heating in air but does'not'melt and is relatively mix.

toxic and non-corrosive.

Because of the many variations in the chemical coniposition of clays and shalesythe most eflfectiveadditiv'e combination varies slightly, from one clay to another.

I have found that wherecoring conditions are not *too'severe, hexamine may be used separately as an effective additive. However, where conditions are moresevere, I have found that it is preferable to use a combination of hexamine with an inorganic-ammonium salt. The optimum additive combination appears to-be hexamin'e and ammonium nitrate. This additive combination, when usedwith various shalesand' clays, such as surface claysor fire clays, is very effective in controlling coringin kilnefired P oducts, 7 1

- The. total amount of additive or additive combination need -not-exceed a concentration of about 3% by weight -o fthe' dry clay. 'Amounts excess of 3% may beused; however, increasedamounts apparently do not increase the desired effects proportionately; Thus, when hexai' .3 8S a single additive, theconcentration be the range of .oo1%" to 3%,. a For additive geombinations, thejconcentration can be in the, range of .00l%

ii in 1% qt hexainine in c o'mb'ination' with ,o'o5% to; Y 5% of an inorganic ammonium salt, such as ammonium nitrate, ammonium chloride, ammonium sulfate and ammonium phosphate. When hexamine is used as a single additive, the preferred concentration is 125% toal%',- based on drycla y. Whenan additive combination is used, the preferred concentration is (a) from .0196 to".5% (based on dry clay) of hexamine in combination withXb) from 01% to 1% (based on dry clay) of the inorganic ammonium salt.

With additive combinations, the ratio ofinorganic salt (preferably ammonium nitrate) to hexamine may vary over a wide range. Generally speaking, I have found that there should be an "excess of the inorganic ammonium salt to the hexamine. I have further found that an ammonium salt to hexamine weight ratio in the range of about lzl to' about :1 results in a very 'lfioctive additive combination, with even higher ratios (up to-about 80:1) being workablein many cases.

7 It is apparent that more than one inorganic ammonium salt may be used inthe additive combinations ofthis invention. Thus, such an additive combination may, for example, include a mixture of ammonium nitrate and ammonium sulfate together with hexamine. Because of this, the term inorganic ammonium salt" is intended "to comprehend the salts individually as well as apparent mixtures of them. Other equally obvious equivalences are also intended to be included.

I "The additive and additive combinations of this inven- 'tion areall crystalline solids, providing a stable mamin with negligible vaporprcssure under ordinary conditions. These solid materials are free-flowing and 'e'a sily packaged and handled. In the practice of invention, the'dry additive or additive combination may be added in the'proper amount to thedry clay or shale-before mixing with water or, since the additive and additive combinations are water soluble, a water solution of known concentration and composition may first be prepared and the solution introduced in the proper amount into the clay mix in the pug mill which is the apparatus in which water and clay are admixed toform mud of the right consistency to befed to'the 'eXtruders or molds 'in which the clay products are formed. These procedures can be readily adapted to the various processes for making clayand shale products such as the soft mud process, thesti fi mud process and the dry press process all ofwhich vary significantly K A f s..

gas fired brickyard The gas burner was fired with a methane-air mixture wherein the air exceeded methane on a volume basis by a ratio of 8 to 1. The 9.5 hour firing cycle consisted of an initial 3% hour period during which the temperature was maintained at 700 C., followed by a second 3% hour period during which the temperature was maintained at 800 C., followed by a 1 hour period d ring which the temperature was maintained at 1000" C, after which time the heating means were turned oif and the furnace allowed to cool n1- urally for the last 1% hour period. However, the door to the furnace was not opened until the end of the 9.5

' hour firing cycle. The temperature in the furnace at the end of the 9.5 hour firing cycle, upon opening of the furnace door, was in the "range of 600 to 700 C.

The rating system for coring in Tables H and H1 is based on the severity of the coring as determined from visual observation. The procedure was as follows: The experimental bricks were broken in half and the cores arted numerically. Both the area and the color of the cores were considered. The higher the number, the larger the affected area. Zero means no coring, while ten means very extensive coring. In addition, letters were used to indicate the extent of the afiected area which consisted of black core (or severe core) and that which consisted of brown core (or milder core).

A,;0/4 brown core and 4/4 black core B il1 4 brown core and 3/4 black core C=2l4 brown core and 2/4 black core -D=3/4 brown core and 1/4 black core E=4/4 :brown core and 0/4 black core 'Ihenumber indicating the rating only relates to the only by the water content of the mud fed into the clay ,product forming unit. 7 h

The following examples clear-1y illustrate the-methandcompositions of this invention. I The raw shale used in these experiments produced buff-colored clay products when fired and had 'an .anralys s by e ht p centas shown in Table I.

. on ignition 0m shale at aoo o.

I .Determlned from-a mixture oi6g.-shalein bumLwatcr.

Cylindrical test bricks 1%" in diameter and 1%" ,long, containing the additives, werepressed from the raw shale in a hydraulic press. One blank brick, consurface affected with brown or black core, whereas the .letter indicates the part of that area that is black. .While a considerable amount of brown core can be tolerated, a small amountof blackcore may substantially detract from the quality of a brick. Consequently -It.

.reading of 'SE indicates ,a better condition than a reading of 4D, which in turn is better than 3C, 2B, or 1A,

All E's show a goodcondition (no black core) whereas all'Ds show a condition that is-acceptable.

In Tables 11 and 1H,, experimental data is set out it! .bricks which were compared in the above-described manner. In many cases. bricks containing the same amount and ki d of additives were run through the same firing cycles at different times to reflect duplication of results. Series A shows data for the bricks initially run while series B and'C show data for the-duplicates. containing ';no additives were run in conjunction with :bricks containing udditivcsto serve as checks. These Blanks blanks were iden ical in every respect to the test bricks f taining no additivg was fired for every additive brick.

, in each experiment. A 9.5 hour firing cycle was used the maximum temperature was 1000' C. In all of 'the"examples, the firing-was done-inan electric mufile "furnace which was modified in that a gas burner was built into the door of the: furnace to supply additional 1 iheat'andj to create within the furnace an atmosphere which simulated the atmosphere normally'found in a except for additive content.

Table II sets out experimental data for bricks con taining hexamine alone as an additive. By comparing the blanks with the additive-containing bricks, it can readily be seen that coring was substantially reduced in .eachadditiveecontaining brick.

Table II a 00 t Additive Percent "rage mm SeriesA- Series .1 as ut Do .g .2 as. as Do .4 4E m .Blank. 9a (A .Iable 111 sets out-experimental data for bricks containing additive combinations of various ratios of hexamine wi h ammonium nitrate. Again, it can readily 'be s en that coring was'substantially. reduced in each is additive-containing brick.

Table III Additive Combination Average CoreRating Additive Percent Additive Percent SerlesA SeriesB Series Hexamine .02 NH4NO3 .2 4E 1E Do .02 NH4N0: .4 8A 5A- 9A 7A NH4NO: .2 6A 5E NHINO5 4 6A 1E 9A 7A NHiNOi .3 7 8 9. 5 10 NH4NOa 3 6E 8A NH4NO3 .1 4E 4E NH4NOs .2 6A 5E NH4NO; .4 5A 1E 9A 7A NHNOS .3 "6E 8A NHLNO! .1 513 all NHLNO: .2 5A IE 0 NH4NO; .8 2 NH4N0| .4 0 0 9A 7A 7 Hexamine .3 N'H4N0a .2 1. I;

1 Certain ratings were made on numerical basis only.

tially reduced, providing a ware which possesses. better .dimensional properties.

The following procedure was used in determining the wet strength of the additive containing mud: Small V2" diameter by 2%" rods of the wet mud were extruded by means ofa hydraulic press and the wet strength determined by suspending the rod from two points and applying pressure to its center.

.The weight required to bend the rod a predetermined distance in a given time was used as a measure of. wet strength.

In Table IV, experimental data isset out showing the wet strength of additive-containing bricks and blanks containing no additives. Series B and C were duplicates of the initial run, which is-representedas series A.

clay products from such products. w I .1;

,2. The method of manufacturing improved, clay prod; ucts which comprises adding to theclay mix from which the clay products are formed an additive combination consisting essentially of (a) from .00l% to 1%v by weight (based on dry clay) of hexamethylenetetramine and (b) from .005% to 2% by weight (based on, dry clay) of a member of the group consisting of ammonium nitrate, ammonium sulfate, ammonium chloride, ammonium phosphate and mixtures thereof;- forming clay products from such admixture; and .firing the clay products.

3. The method of claim 2'wherein the additive com? bination is- (a) from .00l% to 1% by weight.(based on dry clay) of hexamethylenetetramine and (b) from ;005% to 2% by weight (based on dry clay) of ammonium nitrate.

4. The method of claim 2 .Whereinthe additive combination is (a) from-01% to .5% byxweight (based on dry clay) of hexamethylene tetramine and (b). from .01%'to 1% by weight (based on dry clay) of ammonium nitrate. J V z 5. The method of ;manufacturing improved clay .products which comprises adding .to the clay mix from which the clay products are formed from .00l% to 3% by weight (based .on dry clay) of hexamethylenetetramine; forming clay products from such admixture; and firing the y Products.

- 6. The method of claimv 5- wherein the additive is from .05% to 1% by weight (based .on dry clay);.,o hexamethylenetetramine.

7. Anew additive for improving adm xmreran th the clay clay products consisting essentially of one part by'weight hexamethylenetetramine and about one to about ten partsoby weights ammonium nitrate. l r

8. A new additive for improving clay products co'nsisting essentially of one partby. weight-hexamethylenetetrami-ne and about oneto about ten parts by weight of a member selected from the group consisting of ammonium, nitrate, ammonium. sulfate, ammonium phosphate and mixtures thereof. 1v

9. The method of improvingvthe wet strength of clay products .during their manufacture priortofiring which comprises adding to the clay mix fromtwhichtheclay Table IV SeriesA SeriesB Series C H20 L Additive Content,

percent Bending Breaking Bending Breaking Bending Breaking Strength Strength Strength Strength Strength Strength In gms. in gms. in gms. in gms. in gms. in gms.

.05% Hexamine .3% NHiNO m- 18.2 119 190 120 188 Blank 18. 2 92 161 70 17 .05% Hexamine 3% NHrNO 19. 6 82 111 83 99 Blank 19. 6 51 95 59 85 It can readily be seen that the additives of this invention are eifective in toughening the mud.

The detailed description and examples given herein are not to be construed as limiting the scope of this invention, and all modifications apparent to those skilled in the art are intended to be included.

I claim:

1. The method of manufacturing improved clay products which comprises adding to the clay mix from which the clay products are formed an additive consisting essentially of a member selected from the group consisting of (1) from .00l% to 3% by weight (based on dry clay) of hexamethylenetetramine and (2) an additive combination consisting of (a) from .001% to 1% by weight (based on dry clay) of hexamethylenetetramine and (b) from .005% to 2% by weight (based on dry clay) of a member of the group consisting of ammonium nitrate, ammonium sulfate, ammonium chloride, ammonium phosphate and mixtures thereof; forming products are formed from .00l% to 3% by weight (based on dry clay) of hexamethylenetetramine.

10. The method of improving the wet strength of clay products during their manufacture prior to firing which comprises adding to the clay mix from which the clay products are formed an additive combination consisting essentially of from .001% to 1% by weight (based on dry clay) of hexamethylenetetramine and from .005% to 2% by weight (based on dry clay) of a member selected from the group consisting of ammonium nitrate, ammonium sulfate, ammonium chloride, ammonium phosphate and mixtures thereof.

11. The method of claim 10 wherein the additive combination is from .00l% to 1% by weight (based on dry clay) of hexamethylenetetramine and from .005% to 2% by weight (based on dry clay) of ammonium nitrate.

12. The method of manufacturing improved clay products which comprises adding in the form of an aqueous solution to the clay mix from which the clay products are firmed a'n-additive-eonsisting essentially of a member selected from the group consisting of 1) from-s005% tp'}3 %1iy=weight2 (baled dry clay} 9f hexam'ethyleneand (2) an 'ndditive combination consisting of (a) from 901% to 1% by weight (based on dry clay) hthexamethylenetetramine and (b) from .005% to 2% hyweight (based on dryclay) of a member ofthe group consisting of ammonium nitrate, ammonium sulfate, ammonium chloride, phosphate and mixtures thereof; formin'gelayproducts'trom such admixtures; and firing'the clay-pnoducts.

13. method of manufacturing improved clay prodwhich'oonaprises adding iii-the form of an aqueous "solution '10 be clay mix from which the clay products ore formed an additive combination consisting essentially of (a) from 0195 to 1 by weigh t (based on dry clay) of hexamethylenetetramine and (b) from .005.%to 2% by weight (based on dry clay) of a member of the group consisting of ammoniumnitrate, ammonium sulfate, ammonium chloride,- ammonium phosphate and mixtunes thereof; forming clay products from such admixture; and firing the clay products. 7

14. The method of manufacturing improved clay products which comprises adding in the form of an'aqueous solution to the clay mix from which the clay products sre formed an additive combination consisting essentially of (a) from .001% to 1% by weight (based on dry clay) of hexamethylenetetraminel and (b) from -'.00$% to 2% byweight (based on dry clay) of ammoninm nitrate; forming clay products from such admixture; and firing the clay products. 15. The method ofmanufacturing improved clay products which comprises adding in the form of an aqueous -solution to the clay mix from whichthe clay products are formed from 001% to 3% by weight (based on dry lay) of hexamethylenetetramine; forming clay products *from such admixtuu; and firing the clay products. 16. A new additive for improving clay products con- -sisting essentially of an aqueous solution of one part by weight of hexamethylemetetramine and about one to about ten parts by weight of :a' member selected from the group consisting of ammonium nitrate, ammonium sulfate, ammonium-phosphate and mixtures thereof.

17. A new additive for improving clay products consisting essentially of an aqueous solution of about one to about ten parts by weight of ammonium nitrate and one 7 part by weight of hexamcthylenetettamine.

18. The method of manufacturing improved clay prod ucts which comprises adding tolthe clay mix from which the clay products are formed an additive consisting es.- scntialiyof a member selected from thegroup consisting-of (1) from .001% to 3% by weight (based on dry clay) of 'hexamethylenetetramine and (2) an additive combination consisting of (a) from .001% :to 1% by .weight (basedon dry clay) of hexamethylenetetramine and (b). from .005% to 2% by weight (based on dry :clay) of an inorganic ammonium salt; forming clay products-from such admixture; and firing the clay products. i 19. The method or improving the wet strength of clay products during theirmanufacture prior to firing which comprises adding to the clay mix from which the :clay products are formed an additive consisting essentially ofa member selected from the group consisting of :(lljrom 0 01% to 3%byweight (based on-dry clay) of hexamethylenetetramine and (2) an additivefcombinationconsisting of (a) from .001% to 1%"by Weight (based on dry clay) of hexamethylenetetraniiiieiand (b) from .005 to 2% byvveight (based on dry clay) of an inorganic-ammoniumsalt. If" i 20. The method of manufacturing improved clay prodhcts' which comprises'adding in the form of an aqueous solution to the clay mix from which the clay products are formed an additive consisting essentially of a member selected from the group consisting of 1) from .-00l% to 3% by weight (based on dry clay) of hexamethylenctetramine and (2) an additive combination consisting of (a) from 001% to 1% by weight (based on dry clay) of hexamethylenetetramine and (b) .005 to 2% by weight' (based on dry clay) of an inorganic ammonium s'altfforming'clay products from such admixture; and ffiring the clay products.

References'fiited in the file of this patent I) i r UNI IE1) STATES PATENTS }.1, 719,1ss" Chamberlain July 2, 1929 2,5 62,5 49 Hatch July 31, 1951 2,838,410 Francis IunelO, 1958 FOREIGN PATENTS {258,909 Switzerland 1950 s OTHER REFERENCES Modern Drug Encyclopedia & Therapeutic Index, 6th

ed., pub. 1955 (page 1114).

Beilsteins Handbuch der Organischen Chemie, vol 26,

second supplement 1952 (page 201). 

1. THE METHOD OF MANUFACTURING IMPROVED CLAY PRODUCTS WHICH COMPRISES ADDING TO THE CLAY MIX FROM WHICH THE CLAY PRODUCTS ARE FORMED AN ADDITIVE CONSISTING ESSENTIALLY OF A MEMBER SELECTED FROM THE GROUP COSISTING OF (1) FROM .001% TO 3% BY WEIGHT (BASED ON DRY CLAY OF HEXAMETHYLENETETRAMINE AND (2) AND ADDITIVE COMBINATION CONSISTING OF (A) FROM .001% TO 1% BY WEIGHT (BASED ON DRY CLAY) OF HEXAMETHYLENETETRAMINE AND (B) FROM .005% TO 2% BY WEIGHT (BASED ON DRY CLAY) OF A MEMBER OF THE GROUP CONSISTING OF AMMONIUM NITRATE, AMMONIUM SULFATE, AMMONIUM CHLORIDE, AMMONIUM PHOSPHATE AND MIXTURES THEROF; FORMING CLAY PRODUCTS FROM SUCH ADMIXTURE; AND FIRING THE CLAY PRODUCTS. 